Silk realized that the energy from this newly formed quasar would create intense temperature changes in the surrounding gas. This would cause the gas around the black hole and its newly formed quasar to condense into stars, which means, in effect, that the black hole could have helped to trigger the birth of the galaxy.

We think of black holes normally as being destructive influences on their surroundings. In this case they're creative, they're having a very positive impact on the formation of the galaxies.

But there was more. This theory predicted when and why the black hole would eventually stop feeding and go quiet. They calculated that this would happen when the feeding black hole grew so large that the vast amount of energy spewing from its bright quasar would literally force the rest of the galaxy out of its reach.

It has the effect of pushing (in) a wind against the surrounding gas and driving the surrounding gas away like a snowplough?

With only its hot whirling quasar within its reach, the black hole would swallow that up and then stop feeding. It would be left invisible at the center of the galaxy. Silk and Rees calculated that this moment when the black hole pushed the surrounding galaxy away would depend bizarrely on how fast the stars in the outer galaxy were moving. The faster these stars were circling, the harder it would be to push them away and the bigger the black hole would need to grow to produce enough energy to overcome the motion of the circling stars, which means the size of the black hole in the end depends on how fast the stars are moving in the newly formed galaxy around it.

If our theory is correct, there should be a simple relation between the mass of the central black hole and the speed or the sigma of the stars in the newly formed surrounding galaxy.

And this is exactly what has just been found.

spew: expel or be expelled in large quantities rapidly and forcibly

snowplough: an implement or vehicle for clearing roads of snow